Hawaii's development over the past few centuries has largely centered on agriculture -- especially pineapple and sugar cane. Today the favored crop seems to be tourists, of which there is no shortage.
Sadly, not many crops are grown in Hawaii anymore except produce that is consumed by the local population. The exception is Maui which still grows a significant quantity of sugar cane. The legacy of the old sugar towns lingers and you can see remnants of them when you travel around the islands, like this abandoned sugar mill in Koloa (near the south shore of Kauai).